The present invention relates to the general field of turbo-propeller (turboprop) engines equipped with two counter-rotating propellers driven in rotation by means of a single turbine. It relates more particularly to a mechanical transmission device used between the turbine rotor shaft and the two shafts for driving the two propellers in rotation.
In known fashion, a dual-propeller aircraft turboprop includes two counter-rotating unshrouded fan blade sets. In certain dual-propeller turboprop architectures, these fan blade sets are driven in rotation by a power turbine having two counter-rotating rotors. In other architectures more particularly related to the present invention, the fan blade sets are driven by one and the same rotor of the power turbine. Reference can be made for example to document FR 2,942,203 which describes an example of implementation of such an architecture.
The counter-rotating propellers of such a turboprop can be driven in rotation directly or indirectly through a mechanical transmission device constituting a speed reducer and including in particular an epicyclic gear train. Generally, this epicyclic gear train comprises in particular a sun gear shaft which is centered on the longitudinal axis of the turboprop and which is connected upstream to the power turbine rotor to be driven thereby. Downstream, this sun gear carries the sun gear of the epicyclic gear train and transmits through gears its rotary motion to the two sets of fan blades of the turboprop.
In operation, the turboprop undergoes distortions which can extend to the mechanical transmission device. Now if these distortions reach the epicyclic gear train of the mechanical transmission device, they threaten to cause misalignment of the different planet gears which constitute it, which then brings about premature wear of the teeth of these planet gears.